1. Field of the Invention
The present invention relates to a semiconductor device, and more particularly, to a semiconductor device having a resistor, a bleeder resistance circuit employing a resistor and a semiconductor device including the bleeder resistance circuit.
2. Description of the Related Art
Up to now, resistors formed from a semiconductor thin film such as polysilicon or bleeder resistance circuits using the resistors have been employed in many cases, and there is such a well-known product that is formed from a semiconductor thin film of either N-type conductivity type or P-type conductivity type. Normally, a gate electrode of a MOS transistor is formed from an N-type polysilicon thin film. In some cases, a so-called homopolar gate electrode is well-known, in which an N-type gate electrode is imparted to NMOS and a P-type gate electrode is imparted to PMOS, in view of placing importance on performance thereof. Also, there is well-known such a method in which a polysilicon fuse is disconnected by being subjected to laser trimming and the connection of a bleeder resistance circuit is changed to obtain a desired voltage division ratio of a voltage. Further, ICs such as a voltage detector and a voltage regulator are fabricated by using the above.
However, when the conventional thin film resistor is subjected to resin-packaging or the like, that is, when stress is applied to the thin film resistor, the resistance value is caused to vary, resulting in that there is a problem in that the bleeder resistance circuit frequently includes the change of the voltage division ratio after resin-packaging. Further, in the conventional laser trimming method, it is necessary to mount a fuse in order to conduct trimming through a laser beam in addition to the bleeder resistance circuit.
The present invention has been made in order to solve the above problem, and an object of the present invention is therefore to obtain a high-precision bleeder resistance circuit, in which an initial resistance value is maintained even after packaging and an accurate voltage division ratio is kept in the bleeder resistance circuit, and to provide a compact and high-precision semiconductor device without the installation of a fuse that has been conventionally required, such as a voltage detector or a voltage regulator with high performance and at low cost.
In a first means that is adopted so as to achieve the above object in a semiconductor device according to the present invention, resistors and resistors of a bleeder resistance circuit employing them are composed of a P-type resistor that is formed from a P-type semiconductor and an N-type resistor that is formed from an N-type semiconductor. Further, the bleeder resistance circuit is characterized in that a resistance value that serves as a single unit is regulated by the resistance value obtained by coupling the P-type resistor with the N-type resistor, thereby offsetting the changes of the resistance values to each other which occur in the P-type resistor and the N-type resistor due to a piezo effect described below.
The description of the change of the resistance value due to the piezo effect and an influence that is exerted on the bleeder resistance circuit will be made below.
When stress is applied to the resistor, the resistance value of the resistor is changed by the so-called piezo effect, and the direction of the change of the resistance value becomes reverse between the P-type resistor and the N-type resistor. This has been confirmed by experiments of the present inventor as well. For example, the resistance value of the P-type resistor decreases and the resistance value of the N-type resistor increases. (The direction of the change is changed in accordance with the direction in which stress is applied.)
When conducting resin-packaging of an IC, stress is generated. Thus, the resistance value of the resistor is changed due to the piezo effect as described the above. The bleeder resistance circuit is constituted so as to obtain an accurate voltage division ratio, however, the resistance value of each resistor is changed, resulting in that the voltage division ratio is also changed.
The resistor according to the present invention is composed of the P-type resistor that is formed from the P-type semiconductor and the N-type resistor that is formed from the N-type semiconductor. Therefore, even when stress is applied, it is possible to prevent the resistance value from being changed. Also, in the bleeder resistance circuit, the resistance value that serves as the single unit is regulated by the resistance value obtained by coupling the P-type resistor with the N-type resistor. Thus, even when stress is applied, the changes of the resistance values of the individual resistors offset each other, thereby being capable of maintaining the accurate voltage division ratio.
A second means that is adopted so as to achieve the above object in a semiconductor device according to the present invention is characterized in that a P-type resistor is disposed at a low potential side and an N-type resistor is disposed at a high potential side, the P-type resistor is separated from the N-type resistor by an insulating film, the resistors remain in a state where a current does not flow as long as no additional action is performed, and a laser beam is irradiated to only a necessary portion of the insulating film portion to destroy the insulating property thereof to thereby achieve conductivity between the P-type and N-type resistors. Accordingly, a fuse that has been conventionally required is unnecessary.
A third means that is adopted so as to achieve the above object in a semiconductor device according to the present invention is characterized in that a gate electrode of a MOS transistor and a P-type resistor are formed of the same polysilicon thin film and a high concentration impurity region of the P-type resistor for making electrical connection with a metal wiring is formed from a polysilicon thin film having the same impurity and impurity concentration as those of the gate electrode of the MOS transistor. Accordingly, the performance of the P-type MOS transistor can be improved at low cost without increasing the number of manufacturing processes.
A resistor of a semiconductor device according to the present invention is composed of a P-type resistor that is formed from a P-type semiconductor and an N-type resistor that is formed from an N-type semiconductor. Therefore, even when stress is applied by resin-packaging or the like, the changes of the resistance values of individual resistors offset each other, thereby being capable of maintaining an initial resistance value. Also, in a bleeder resistance circuit, the resistance value that serves as a single unit is regulated by the resistance value obtained by coupling the P-type resistor with the N-type resistor, thereby being capable of maintaining an accurate voltage division ratio. Further, the P-type resistor is disposed at a low potential side and the N-type resistor is disposed at a high potential side, and the resistors are adjacently arranged via an insulating film. A laser beam or the like is irradiated to an insulating film portion to destroy the insulating property thereof to thereby achieve conductivity between the P-type and N-type resistors. Thus, a fuse that has been required in a conventional manner can be made unnecessary. Still further, a gate electrode of a MOS transistor and the P-type resistor are formed of the same polysilicon thin film, and a high concentration impurity region of the P-type resistor for making electrical connection with a metal wiring is formed from a polysilicon thin film having the same impurity and impurity concentration as those of the gate electrode of the MOS transistor. Accordingly, the performance of the P-type MOS transistor can be improved without increasing the number of manufacturing processes.
When the above bleeder resistance circuit is employed, a compact and high-precision semiconductor device such as a voltage detector or a voltage regulator can be obtained.